1. Field of the Invention
The invention relates to a suction device for a paper machine for producing a paper or cardboard web and a method for vacuuming a web section of a paper machine.
2. Background of the Invention
Suction devices in paper machines are primarily used to vacuum the fabric webs of the paper machine. The fabric webs may be vacuumed either with or without an adhering paper web. One purpose of vacuuming the fabric web is to dehumidify the fabric web and/or the adhering paper web. Such suction devices may also be used to transfer the paper web from one fabric web to another fabric web.
In this context, a "fabric web" typically refers to a felt web or belt. However, the term as used herein shall also encompass forming and drying screens or sieves.
The vacuum pressure that is applied to the suction device creates a normal force between the contact surface of the suction device and the fabric web. This normal force leads to relatively strong friction between the fabric web and the contact surface. Of course, this friction causes considerable wear and tear on the fabric sheet or web and the contact surface.
It is known in the art to reduce the friction by positioning the suction device slightly back from the straight roll-to-roll connection (straight roll connection) within the press unit. The movement or excursion of the fabric web section away from the straight roll connection (due to the suction device) creates a force that acts against the normal force described above, thereby decreasing the friction between the fabric web and the contact surface.
These known suction devices, however, suck air in during their start-up, thus, the felt belt must be placed on the suction device by hand. The need for trained personnel to place the web section on the suction device by hand is labor-intensive and costly.